T214 Lakes of the World Through Time and Space — Archives of Climate, Paleoenvironments, Ecosystems, Geohazards, and Economic Resources

Tuesday, 24 September 2024
1:30 PM - 5:30 PM
213B

TRACING RATE AND EXTENT OF HUMAN INDUCED HYPOXIA DURING THE LAST 200 YEARS IN THE MESOTROPHIC LAKE TIEFER SEE (NE GERMANY)

Paper number: T214-9
Program: Technical Sessions
Time: 3:20 PM – 3:35 PM

Authors

  • Ido Sirota Presenting Author
    GFZ German Research Centre for Geosciences, Potsdam

Abstract

The global spread of lake hypoxia, [O2] < 2 mg/l, during the last two centuries has a severe impact on ecological systems and sedimentation processes. While the occurance of hypoxia was observed in many lakes, a detailed quantification of hypoxia spread remained largely unquantified. We track the evolution of hypoxia and its controls during the past 200 yrs in lake Tiefer See (TSK; NE Germany) using 17 gravity cores, recovered between 10 and 62 m water depth in combination with lake monitoring data. Lake hypoxia was associated by the onset of varve preservation in the TSK, and has been dated by varve counting to 1918±1 at 62 m water depth and reached a lake-floor depth of 16 m at 1997±1. This indicates oxygen concentration to fell below the threshold for varve preservation at the lakefloor (>16 m). Sediment cores at 10-12 m depth do not contain varves indicating well oxygenation of the upper water column. Monitoring data show that the threshold for hypoxia at the depocenter is a period of five months of [O2] < 5 and two months of [O2] < 2 . Detailed TOC, and XRF core scanning analyses of the short cores indicate that the depletion in DO started several decades prior to the varve preservation. This proves a sudden change in the depositional conditions in the lake following a transition phase of several decades during which varve preservation was not accomplished. Furthermore, varve preservation does occur at seasonal stratification and not necessarily requires permanent stratification.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-401386

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